1. Field of the Invention
This invention relates to gas turbine gas generators, and more particularly to structurally compact, high performance gas turbine gas generators using centrifugal compressors and radial inflow turbines. This invention also relates to gas turbine engines using such gas generators.
2. Description of the Prior Art
There is a continuing need for gas turbine power plants as alternatives for diesel engines, for instance, for vehicular and other applications where a compact, lightweight engine is required. Practical experience has shown that substantial space and weight savings are available using conventional gas turbines. However, existing gas turbine engines in the small/medium power range, e.g. about 4 megawatts (“Mw”) or less, typically have thermal efficiencies less than 30%. Heretofore, efficiencies of 30% or greater were only available for axial compressor-axial turbine type engines above about 4 Mw because of the lower relative losses of the larger engines.
Also, while radial-type gas turbine engines having inflow turbines are known, multiple compressor stages are usually required to achieve acceptable thermal efficiencies. However, the relative complexity and other limitations of using multiple compressor stages in existing simple cycle engines continues to be a major drawback in prior art devices, particularly in the small/medium power range, where simplicity is most important.
For example, a known gas turbine auxiliary power unit (APU) includes a double-entry (often referred to as a “dual-entry”), centrifugal compressor first stage and a single-entry centrifugal compressor second stage operating in series to provide compressed air both for combustion with fuel in a combustor and bleed air for external use. The hot gases from the combustor are fed to a single stage radial inflow turbine that drives both compressors and, in addition, provides shaft power for external use in a manner consistent with a single shaft engine.
Also, in previous patents (U.S. Pat. No. 4,641,495 and U.S. Pat. No. 4,704,861), the present inventor disclosed fuel-efficient, simple cycle gas turbine gas generators using a dual-entry first stage centrifugal compressor and a single-entry second stage centrifugal compressor together with a radial inflow turbine in a single shaft configuration. In these gas generators, a total of three rotor components as well as three bearing assemblies are used to mount the shaft assembly to the gas generator housing, with one of the bearing assemblies being positioned in the turbine section. Problems with the increased complexity of such an arrangement are compounded by the higher cost and potentially higher failure rate for the bearing assembly in the turbine section.